The goal of this project is to characterize the role of amino acid compartmentation in the control of arginine metabolism in Neurospora crassa. Arginine and its biosynthetic and catabolic intermediate, ornithine, are sequestered in the vacuoles in this organism. The specificity, kinetics, energetics and regulation of amino acid transport across the vacuolar membrane and its relation to plasma membrane transport systems will be investigated. The effect of environmental alterations on vacuolar pH and the association of vacuolar arginine with polyphosphates will be investigated using in situ 15N-nuclear magnetic resonance spectroscopy. The relationship between nitrogen metabolite regulation and mobilization of vacuolar arginine will be investigated using mutants affecting nitrogen metabolite regulation. Finally, attempts will be made to isolate and characterize mutants impaired in movement of amino acids between the cytoplasmic and vacuolar compartments. The results may provide insight into the function of amino acid compartmentation in eukaryotic cells and organisms.